Sexual Reproduction in Plants

Sexual reproduction in plants is a natural process in which the gamete or sex cell of parents fuses to form a zygote that obtains a new individual. The reproductive organs of plants are located inside the flower. So, we can say that plants make flowers to do sexual reproduction inside them and to safeguard their reproductive parts. The flower is the structural unit for sexual reproduction in plants. Sexual reproduction promotes genetic diversity in a population as the genes of parents are transferred to offspring and mixed during fertilization. The flower is an angiosperm that does sexual reproduction in plants.

Sexual Reproduction in Plants

A flower typically has sepals, petals, one or more stamens, carpels, and receptacles. Some flowers have nectar. The outermost whorl of the flower is known as the calyx (a group of sepals); it protects the interior organs of the flower. Calyx are of different kinds, like the perianth is green and situated below the flower. Glume, the calyx of grasses, encloses one more floret. The corolla contains colorful petals. It also protects the interior part of the flower from heat and helps attract pollinators. In some flowers, nectar or appendages are attached to the corolla. Flowering plants have microscopic gametophytes. Let’s start with the bottom part of the flower which is the pedicel. It takes the whole weight of the flower.

Pedicel

The first part on which the whole burden of a flower is placed is the pedicel. It is a small stalk for supporting the flower of an inflorescence; it is the ultimate division of a common peduncle. The green leaves attached to the pedicel are called Sepal, and the group (whorl) of Sepal is called Calyx.

A typical flower has four floral whorls. Whorls is a rounded or radial arrangment form of 3 or more leaves that form a flower parts. 4 main parts of flower are:

Calyx

The individual leaf-like structure is called sepals. In the diagram given, we have seen two sepals. So, the whorl of these sepals collectively forming the outer floral envelope enclosing and supporting the developing bud is called the calyx. Calyx help to protect the internal part of flower. Sepal protects the flower in bud condition. They are green in color. It means they contain chlorophyll and perform the function of photosynthesis. Receptacles or thalamus is situated at the top of a stem that support head of a flower.

Corolla

In the upper part of the calyx, there are individual petals; the collective form, or whorl, of these petals that form the inner floral envelope is called the corolla. Petals protect the inner part of a flower. It means it protects the male and female parts of a flower. Petals have fragrance, so they attract insects like honeybees, butterflies, and mosquitoes.

Calyx and Corolla are called the outer accessory whorls of the flower. So, they will not take part in the reproduction process. They only protect the inner male and female whorls of the flower.

In the figure given below, both the Male and Female part is present. So, we can say that it is a Bisexual flower. But some flower consist of only Androecium and some consist of Gynoecium. Such flowers are called Unisexual flower.

Androecium

We know that a flower has a male part and a female part. Its male part is called Androecium. Anther and stamens formed the male part of flower. A combination of anther and filament is called stamen and the whorl of these stamens is called Androecium. The filament is a long stalk attached with the anther with two lobes. Each lobes consist of 2 embryo sac. So, anther contain 4 embryo sac type of structure that called as (microsporangia) that help in the formation of pollens.

Gynoecium

The female parts of the flower are called Gynoecium. It is located in the central part of a flower. The female part is made from carpels ot pistils. There can be one or more carpel present in the flower. The carpel is consist of ovary, style and stigma. So, it formed the inner most whorl of the flower. stigma is the sticky part that attract pollens, ovary contain the seeds. The difference between the carpel and pistil is that the pistil contain one or more carpel.

It means all these parts are arranged in a particular order from outside to inside, starting from the calyx and ending at the gynoecium.

Features of Sexual Reproduction in Plants

The reproduction take place in a sequential manner.

1. Gamete formation: Male and female take part in gamete formation.
2. Fusion and Fertilisation: Fusion of gamete takes place to form a zygote. The process called fertilisation.
3. Growth and development phase: At this stage, growth and development of Zygote take place and here the zygote is formed into embryo by the process of Mitosis.
4. Seed Formation: Embryo turned into seed that formed new Individual plant.

Process of Sexual Reproduction

The process of sexual reproduction takes place by the fusion of male and female gametes of opposite sex that help in the formation of young individuals. The male part form pollen and the female part form egg and the fusion of male and female part formed zygote. Zygote then turn into embryo and embryo will turn into seed and then seed will form a new plant. So, let’s talk about each part that take place in reproduction process.

Male Gametophyte or Androecium

Inside the corolla of flowers, we have stamens. The whorl or collective formation of stamens formed androecium. Stamen consist of two parts: one is the anther, and the other is a single-veined stalk or filament. The point that connects the anther and filament is called the connective. A common anther has two lobes, but some have a single lobe. So, it is dithicus, and each lobe has two pollen chambers (pollen sacs). It means there are two four-pollen sacs, and an anther with four pollen chambers is called tetrasporangiate. The pollen chambers have pollen mother cells that form pollen grains, and these are diploid. The male gamete is formed by meiosis. In meiosis, four new cells form that are haploid in nature. The new haploid that forms is called a microspore. These pollen grains are the tiny particles from which we get the male gametophyte (micro-gametophyte). Typically, one pollen grain contains two male gametes.

Female Gametophyte or Gynoecium

The reproductive part of a female is located at its centre, called the carpel. A flower can have one or more than one carpel. These carpels can be separated or united in nature. Here we have a separate carpel in the figure. The upper part of the carpel is called the stigma. Stigma is a sticky or hairy surface that captures the pollen grain. Beside this stigma, we have a tube-like structure called style. The style is a hollow structure from the inside. At last, we have seen a spherical part, which is the ovary. It is located at the base of each carpel. So, we have three basic parts in a Gynoecium stigma, style and ovary.

Pollination and Fertilisation

In the male part of the flower, we have an anther, and it contains pollen grains. When pollen grains form completely, the anther becomes mature. At this time, the anther will burst, and the pollen grains present on the anther will fly in the air. So, some of the pollen get stuck at the female part of Stigma.

It means at this stage there will be a transfer of pollen grain from another to stigma. This process is called pollination. During pollination, the stigma becomes sticky. This stigma forms a sugary serum or liquid that makes it sticky so that it can attract pollen. Now these pollen gradually start to grow or germinate when they fall upon the sticky stigma.

Inside carpel and in ovary we have some tiny particles, these tiny particles are called ovules that formed on the inner ovary wall. An ovary can have one or more than one ovule.

Ovule

Each ovule consists of a female gametophyte, which is a small bag-like structure called an embryo sac. The embryonic sac is formed by the process of meiosis, and all the cells that are present in the ovule are formed by meiosis. In a cell, we have two nuclei called polar nuclei that are present in the centre of the embryonic sac. Both polar nuclei are haploid and consist of one set of chromosomes. At last, we have a pink cell; this pink cell is an egg cell. The egg cell is the female gamete. So, a single egg cell is present in the ovule. The two orange cells that are present beside the egg cell are called synergids. So, these are the cells present inside the embryo sac. In the upper portion of the ovule, we have three green-colored cells. These are called antipodal cells, or antipodals.

Germination

It is the process by which the pollen grain delivers sperm cells to the embryonic sac by means of a pollen tube. This tube passes through the style to the bottom of the embryo sac. We have studied that pollen grains have two male gametes. The pollen tube carries these male gametes to the embryo sac. These male gametes travel through the pollen tube to get into the ovary.

At this stage, the tip of the pollen tube bursts and the male gamete is released inside the embryonic sac. One male gamete (sperm cell) will unite and fertilise the egg cell to form a zygote. So, the fusion of the sperm cell with the egg cell forms a zygote, and this process is called fertilisation. The other male gamete will unite with the two polar neuclei and form a new cell called the endosperm. So, fertilisation takes place twice. The first time, the formation of zygote takes place, and the second time, the formation of endosperm takes place. So, this is called double fertilization.

What will Happen After Fertilisation?

After fertilisation, the ovules develop into seeds. The petals will dry and fall off, and the ovules present inside them will grow to become seeds until they get favourable conditions for germination. The zygote develops into an embryo, which remains dormant in the seed until the conditions are favourable for germination. Ovules turn into seeds, and the ovary wall, along with the encapsulated seeds, develops into a fruit.

Important Point

Pollen allergy-allergic rhinitis in every spring and summer: Flowering plants release pollen grains and these pollens from different plants have differences in their wall proteins. Some people are allergic to these pollens. This results in a profusely running nose, reddened and itchy eyelids, congestion, and sneezing. This is also called hay fever.

FAQ’s – Sexual Reproduction in Plants

1. What are the Types of Reproduction in Plants?

The process of producing offspring is called reproduction. There are two type of reproduction in plants Sexual and Asexual. Fusion of male and female gamete is called sexual reproduction. The male gamete transfer pollen grains from anther to the female part stigma in sexual reproduction.

2. What are the Examples of Asexual Plants?

With the help of roots, stems, leaves and buds asexual reproduction takes place. Some example of asexual plants are like potato ( a stem), onion, ginger, dahlia etc. Grafting and budding are the most famous example of asexual plants. Grafting is most often done with fruit trees like citrus and mangoes trees to produce new and improved varieties.

3. Are Flowers Asexual?

Flowers and angiosperm plants that obtain by the sexual mode of reproduction and non-flowering plants are gymnosperm that formed by seeds or asexual mode. In asexual reproduction the plants are formed with the help of buds, stems, leaves and buds. Some method of asexual plants are grafting, vegetative propogation, Micropropagation, layering etc.

4. Is Pollination Asexual?

No, pollination is not asexual. It is the process of sexual reproduction in which the pollens are transferred from anther to stigma. Pollination is of 2 types- self pollination and cross pollination. In self pollination the pollen grains are transferred from anther to stigma in same flower and in cross pollination the pollen grains of a flower is transferred to the stigma of another flower.

5. Do all Flowering Plants shows Sexual Reproduction?

An angiosperm is a flowering plant that have stems, roots and leaves. These flowering plants produce seeds by the process of pollination. It means that all the flowering plants shows sexual reproduction.